1. Field of the Invention
The present invention relates to a printer for printing on a sheet. The printer of the present invention is generic name of a device comprising: a sheet sending mechanism which successively sends cut sheets; and a printing mechanism which successively prints characters, graphics, photographic images or the like on the sheets sent by the sheet sending mechanism. Not only a printer with a single function, but also a copying device, a facsimile device, a composite device (or a multifunction device) and the like comprising the sheet sending mechanism and printing mechanism also are the printer described herein.
The printer of the present invention automatically selects a control procedure of returning a sheet, which is subsequently taken out from a cassette, to the cassette, and a control procedure of discharging the subsequent sheet to the outside of the printer, when printing data for the subsequent sheet no longer exists in the middle of sending the cut sheets successively.
2. Description of the Related Art
There has been developed a printer which takes a piece of sheet from a cassette having a plurality of cut sheets stacked thereon, sends the sheet to a printing region via a sheet guide, and prints on the sheet while the sheet passes through the printing region. This type of printer comprises a supply roller in order to take a piece of sheet from a cassette and send it to a sheet guide.
There has been developed a printer in which a pair of feed-in rollers are disposed on an upstream side of the printing region in order to adjust a distance between a front edge of each sheet and a print starting position to a predetermined distance. When the pair of feed-in rollers rotates in a rearward direction, a sheet, which is sent by the supply roller, cannot enter between the pair of feed-in rollers. Here, the rotation in a rearward direction means that the pair of feed-in rollers rotates in a direction of sending a sheet toward a sheet guide. When a sheet is sent by the supply roller toward the pair of feed-in rollers which rotate in the rearward direction, the front edge of the sheet is aligned with a contact line with which the pair of feed-in rollers contact. The pair of feed-in rollers rotating in the rearward direction exerts a function of positioning the front edge of the sheet to a fixed position. In this state, when the pair of feed-in rollers starts to rotate in the forward direction, the front edge of the sheet is aligned with a fixed position and then the sheet is sent to the printing region. By controlling the printing mechanism on the basis of the timing at which the pair of feed-in rollers starts to rotate in the forward direction, the position of the sheet sent by the pair of feed-in rollers and the timing for operating the printing mechanism are adjusted to a preset relationship. By disposing the pair of feed-in rollers on an upstream side of the printing region, the distance between the front edge of each sheet and the print starting position can be adjusted to the predetermined distance.
When the sheet is sent toward the pair of feed-in rollers rotating in the forward direction, the front edge of the sheet is aligned with the contact line with which the pair of feed-in rollers contacts, even if the front edge of the sheet sent by the supply roller is inclined, thus the inclination of the front edge is compensated.
In the case of a printer comprising the pair of feed-in rollers, it is necessary to form an appropriate space between the back edge of a preceding sheet sent by the pair of feed-in rollers and the front edge of a subsequent sheet sent by the pair of feed-in rollers. Therefore, a technology of intermittently rotating the supply roller is known.
Japanese Patent Application Laid-Open Publication No. 2002-283637 (particularly, FIG. 2, FIG. 4, and the paragraph 0085) discloses a technology of suitably controlling a space between a preceding sheet and a subsequent sheet in a case of high-quality printing and a case of high-speed printing. In the technology disclosed in Japanese Patent Application Laid-Open Publication No. 2002-283637, if the printing data to be printed on the subsequent sheet no longer exist, the sheet is stopped in a state in which it is sent to the printing region. If a printing operation is not executed on the sheet within a certain period of time from the stoppage of the sheet, the sheet sent to the printing region is returned to a paper tray.
Japanese Patent Application Laid-Open Publication No. 2001-206566 (see FIG. 1 and FIG. 4) discloses a printer in which sheets, which are stacked within a paper cassette, are held between a supply roller and a friction pad, whereby only one of the sheets is taken out and sent toward a sheet guide. In the printer disclosed in Japanese Patent Application Laid-Open Publication No. 2001-206566, the supply roller is rotated in the rearward direction every time when a single sheet is separated by the supply roller. Therefore, the sheet drawn to the outside of the paper cassette is returned into the paper cassette.